Simple thermotunnel device comprising two metallic electrodes separated by vacuum gap has energy diagram shown in FIG. 1 (image charge modification of the barrier shape is omitted for simplicity). 10 and 12 are metallic electrodes separated by a distance d0 in a vacuum (U.S. Pat. No. 6,417,060; WO99/13562). The cooling power and efficiency of such devices have been calculated by Hishinuma et al. [Appl. Phys. Letters (2001) 78(17):2572-2574], who show that that electrons having a wide spectrum of energies take part in heat pumping. Thus, both electrons 14 sitting at low energy levels (around the Fermi level, fe) and electrons sitting at higher energy levels 16 take part in tunneling through the potential barrier and transfer heat from electrode 10 to electrode 12 (see FIG. 1; for simplicity it is assumed that work functions, Φ, of two electrodes are equal and equal to applied voltage eV bias). Tunneling of low energy electrons leads to low efficiency heat pumping. Pumping of low energy electron requires the same work from external source as pumping of high energy electron (eVbias in both cases). At the same time low energy electrons remove less heat from the emitter than high energy electron. Besides that in some cases tunneling of low energy electron might cause negative heat flow.